Method for on-press developing high speed laser sensitive lithographic plate

ABSTRACT

A method of on-press developing a high-speed laser sensitive lithographic printing plate with ink and/or fountain solution is described. The printing member comprises on a substrate a photosensitive layer soluble or dispersible in ink and/or fountain solution and capable of hardening upon exposure to a laser. The plate is exposed with a laser and on-press developed with ink and/or fountain solution. At least a portion of the on-press development is performed with the plate under a yellow-red light or in substantial darkness.

FIELD OF THE INVENTION

This invention relates to lithographic printing plates. Moreparticularly, it relates to on-press ink and/or fountain solutiondevelopment of high-speed laser sensitive lithographic plates having ona substrate a photosensitive layer that has limited stability in ambientroom light.

BACKGROUND OF THE INVENTION

Lithographic printing plates (after process) generally consist ofink-receptive areas (image areas) and ink-repelling areas (non-imageareas). During printing operation, an ink is preferentially received inthe image areas, not in the non-image areas, and then transferred to thesurface of a material upon which the image is to be produced. Commonlythe ink is transferred to an intermediate material called printingblanket, which in turn transfers the ink to the surface of the materialupon which the image is to be produced.

At the present time, lithographic printing plates (processed) aregenerally prepared from lithographic printing plate precursors (alsocommonly called lithographic printing plates) comprising a substrate anda photosensitive coating deposited on the substrate, the substrate andthe photosensitive coating having opposite surface properties. Thephotosensitive coating is usually a photosensitive material, whichsolubilizes or hardens upon exposure to an actinic radiation, optionallywith further post-exposure overall treatment. In positive-workingsystems, the exposed areas become more soluble and can be developed toreveal the underneath substrate. In negative-working systems, theexposed areas become hardened and the non-exposed areas can be developedto reveal the underneath substrate. The exposed plate is usuallydeveloped with a liquid developer to bare the substrate in thenon-hardened or solubilized areas.

On-press developable lithographic printing plates have been disclosed inthe literature. Such plates can be directly mounted on press afterexposure to develop with ink and/or fountain solution during the initialprints and then to print out regular printed sheets. No separatedevelopment process before mounting on press is needed. Among thepatents describing on-press developable lithographic printing plates areU.S. Pat. Nos. 5,258,263, 5,516,620, 5,561,029, 5,616,449, 5,677,110,5,811,220, 6,014,929, 6,071,675, and 6,482,571.

Conventionally, the plate is exposed with an actinic light (usually anultraviolet light from a lamp) through a separate photomask film havingpredetermined image pattern that is placed between the light source andthe plate. White capable of providing plate with superior lithographicquality, such a method is cumbersome and labor intensive.

Laser sources have been increasingly used to imagewise expose a printingplate which is sensitized to a corresponding laser wavelength. Thisallows the elimination of the photomask film, reducing material,equipment and labor cost. Suitable lasers include infrared lasers (suchas laser diode of about 830 nm and NdYAG laser of about 1064 nm),visible lasers (such as frequency-doubled NdYAG laser of about 532 nm,violet laser diode of about 390-430 nm), and ultraviolet laser (such asultraviolet laser diode of about 350 to 370 nm). Among them, infraredlaser diode, violet laser diode, and ultraviolet laser diode are mostattractive. Infrared laser sensitive plates have the advantage ofrelative white or yellow light stability, violet laser sensitive plateshave the advantage of low imager cost due to the low cost of the violetlaser diode which is made in mass production for DVD, and ultravioletlaser sensitive plates have the advantage of higher sensitivity(requiring less laser dosage) than longer wavelength lasers.

Laser sensitive plates generally have higher sensitivity (thanconventional film based plate) because of the limited laser power andthe desire for fast imaging speed. Accordingly, photosensitive platesdesigned for laser imaging generally have limited room light stability.For example, before being developed to remove the non-hardened areas,frequency-doubled NdYAG laser sensitive plates usually require red roomlight for handling, violet laser sensitive plates usually require orangeor yellow room light for handling, and infrared laser sensitivephotopolymer plates usually require yellow room light for handling andhave only limited white light stability (due to, for example, the use ofcertain initiator which has spectral sensitivity in the ultravioletregion).

Such limited room light stability is an inherent barrier for the designand use of on-press developable laser sensitive lithographic platebecause the pressrooms are generally equipped with white lights, inaddition to the difficulties in designing any on-press developable platewith good press performance (including film based on-press developableplate). Despite of such difficulties, there is a strong desire todevelop a high speed laser sensitive on-press developable lithographicplate as well as methods of using it because of its environmental andeconomic benefits.

SUMMARY OF THE INVENTION

According to the present invention, there has been provided a method oflithographically printing images on a receiving medium., comprising inorder:

-   -   (a) providing a lithographic printing plate comprising (i) a        substrate; and (ii) a photosensitive layer soluble or        dispersible in ink, and/or fountain solution and capable of        hardening upon exposure to a laser having a wavelength selected        from 200 to 1200 nm;    -   (b) imagewise exposing said plate with said laser to cause        hardening of the photosensitive layer in the exposed areas;    -   (c) developing said exposed plate with ink and/or fountain        solution on a lithographic press to remove the non-hardened        areas of the photosensitive layer; and    -   (d) lithographically printing images from said plate to the        receiving medium;    -   (e) wherein at least a portion of the on-press development        (step c) is performed with the plate under a yellow-red light,        under a lighting that contains substantially no radiation below        a wavelength selected from 400 to 650 nm, or in substantial        darkness.

Preferably at least 90% (in terms of time) of said on-press development(step c) is performed with the plate under a yellow-red light; and atleast a portion (in terms of time), preferably at least 90%, of saidlithographic printing (step d) is performed with the plate under whitelight or under a lighting with substantial radiation below a wavelengthselected from 400 to 650 nm. More preferably, at least 99% of saidon-press development is performed with the plate under a yellow-redlight and at least 99% of said lithographic printing is performed withthe plate under white light. Most preferably all said on-pressdevelopment is performed with the plate under a yellow-red light, andall said lithographic printing is performed with the plate under whitelight.

The controlled lighting (including yellow-red light) allows handling andon-press developing the plate without causing undesirable hardening inthe laser-non-exposed areas and the yellow-red light also allows theoperator to handle the plate and operate the machines before and duringon-press development with reasonable lighting (although not fulllighting); while the white light during printing allows the operator toinspect the printed sheets under normal lighting.

According to another aspect of the current invention, the above on-pressdevelopment (step c) and lithographic printing (step d) are performed ina pressroom having a yellow-red light source and a white light source;the yellow-red light source is on and the white light source is offduring at least a portion (in terms of time) of step (c), and the whitelight source is on (with the yellow-red light source off or onepreferably off) during at least a portion (in terms of time) of step(d). Preferably, the yellow-red light source is on and the white lightsource is off during at least 90%, more preferably at least 99%, andmost preferably all of step (c). and the white light source is on duringat least 90%, more preferably at least 99%. and most preferably all ofstep (d). Further preferably, the yellow-red light source is turned onand the white light source is turned off at or before the start of step(c), and the white light source is then turned on (with or without theyellow-red light source being turned off) around the end of step (c).

According to a third aspect of the current invention, the aboveimagewise exposure is performed on an exposure device (also calledimager), and the above exposure device and lithographic press are in apressroom having a yellow-red light source and a white light source; theyellow-red light source is on and the white light source is off duringat least a portion of the imagewise exposure (step b) and on-pressdevelopment (step c), and the white light source is on (with theyellow-red light source off or on, preferably off) during at least aportion of the lithographic printing (step d). Preferably the yellow-redlight source is on and the white light source is off during at least90%. more preferably at least 99%, and most preferably all of steps (b)and (c), and the white light source is on during at least 90%, morepreferably at least 99%, and most preferably all of step (d). Furtherpreferably, the yellow-red light source is turned on and the white lightsource is turned off at or before the start of step (b), and the whitelight source is then turned on (with or without the yellow-red lightsource being turned off) around the end of step (c).

According to a fourth aspect of the current invention, the above plateis exposed with said laser while mounted on the lithographic press, andthe press is in a pressroom having a yellow-red light source and a whitelight source; the yellow-red light source is on and the white lightsource is off during at least a portion of the imagewise exposure (stepb) and on-press development (step c), and the white light source is on(with the yellow-red light source off or on, preferably off) during atleast a portion of the lithographic printing (step d). Preferably, theyellow-red light source is on and the white light source is off duringat least 90%, more preferably at least 99%, and most preferably all ofsteps (b) and (c), and the white light source is on during at least 90%,more preferably at least 99%, and most preferably all of step (d).Further preferably, the yellow-red light source is turned on and thewhite light source is turned off before mounting the plate on press (astep before step b), and the white light source is then turned on (withor without the yellow-red light source being turned off) around the endof on-press development (step c).

According to a fifth aspect of the present invention, the above plate isexposed with said laser on a laser imager; said imager is connected to aplate cassette for feeding the plate to the imager and is also connectedto a plate collector for collecting the exposed plate; said imager,cassette and collector are shielded with covers so that no orsubstantially no room light or the below-450 nm portion of the roomlight reaches the plate while the plate is in the cassette, imager orcollector, or during the transportation between cassette imager orcollector; and the exposed plate is picked up from the collector tomount to said lithographic press for said on-press development andlithographic printing. Here said imager and press are in a pressroomhaving a yellow-red light source and a white light source; saidyellow-red light source is on and said white light source is off in saidpressroom when a portion of said covers is opened, when the exposedplate is picked up from the collector to mount to said press, or duringat least a portion (preferably substantially all) of said on-pressdevelopment; and said white light source is on (with the yellow lightsource off or on) during at least a portion (preferably substantiallyall) of said lithographic printing.

According to a sixth aspect of the present invention, the above plate isexposed on a laser imager in an imager room, the exposed plate is placedin a light-tight box to transport to a pressroom, and the exposed plateis then picked up from said box to mount to said lithographic press forsaid on-press development and lithographic printing. Here said imager isin a room (imager room) having a yellow-red light source (with orwithout a white light source), and said press is in another room(pressroom) having a yellow-red light source and a white light source;said yellow-red light source in said pressroom is on and said whitelight source in said pressroom is off when the plate is picked up fromsaid box to mount to said press, or during at least a portion(preferably substantially all) of said on-press development; and saidwhite light source in said pressroom is on (with the yellow light off oron) during at least a portion (preferably substantially all) of thelithographic printing.

According to a seventh aspect of the present invention, the above plateis exposed with said laser on a laser imager in an imager room, theexposed plate is transferred (preferably automatically) through alight-tight passage from the imager room into a light-tight box which islocated fully or partially in a pressroom, and the exposed plate is thenpicked up from the box in the pressroom to mount to said lithographicpress for said on-press development and lithographic printing. Here saidimager is in a room (imager room) having a yellow-red light source (withor without a white light source), and said press is in another room(pressroom) having a yellow-red light source and a white light source;said yellow-red light source in said pressroom is on and said whitelight source in said pressroom is off when the plate is picked up fromthe box to mount to said press and during at least a portion (preferablysubstantially all) of said on-press development; and said white lightsource in said pressroom is on (with the yellow light source off or on)during at least a portion (preferably substantially all) of thelithographic printing.

For plate imaged on a laser imager off press, the imager is preferablyconnected to a plate cassette for feeding the plate to the imager forimaging and also connected to a plate collector for collecting theimaged plate; more preferably, the imager, cassette, and collector areshielded with covers which prevent all or substantially all of the roomlight or the below-450 nm portion of the room light (most preferably allor substantially all room light) from reaching the plate while in thecassette, imager, or collector. Certain parts of the covers can beopened to allow loading additional plates to the cassette, picking upone or more imaged plates from the collector, or checking the imagerunder yellow-red lighting (preferably in a room with the yellow-redlight source on without any white light source on).

When both the yellow-red light source and white light source are turnedoff, the above imager room or pressroom is under a lighting that is atleast 10 limes (preferably at least 100 times) weaker than normal officelighting, under a weak yellow-red light (such as light from a yellow-redfiltering window) or in substantial darkness, more preferably insubstantial darkness, and most preferably in darkness; the lighting ofthe room (with both yellow-red and white light sources off) should besufficiently weak (preferably the room is substantially dark and morepreferably completely dark) so that it does not cause hardening of thephotosensitive layer of a non-covered plate within at least 30 minutes.However, the imager room or pressroom preferably has a closed window orshield which is non-transparent and may be opened to allow outside lightor both outside light and outside air in; such window or shield isgenerally closed, and can be opened during the lithographic printing.

At least the hardened areas of the photosensitive layer (at least afteron-press development) exhibits an affinity or aversion substantiallyopposite to the affinity or aversion of said substrate to at least oneprinting liquid selected from the group consisting of ink and anadhesive fluid for ink (fountain solution is a preferred adhesive fluidfor ink). Preferably, the photosensitive layer exhibits an affinity oraversion substantially opposite to the affinity or aversion of saidsubstrate to at least one printing liquid selected from the groupconsisting of ink and an adhesive fluid for ink (both before and afterlaser exposure). More preferably, the photosensitive layer is oleophilic(and hydrophobic) and the substrate is hydrophilic.

The laser used in this invention can be any laser with a wavelengthselected from 200 to 1200 nm (including ultraviolet, visible, orinfrared laser) which is capable of causing hardening of thephotosensitive layer, preferably an infrared laser (750 to 1200 nm) or aviolet or ultraviolet laser (200 to 430 nm), more preferably a violet orultraviolet laser (200 to 430 nm), most preferably a violet laser (390to 430 nm). The plate can be imagewise exposed with a laser on a plateexposure device and then transferred to a lithographic press foron-press development with ink and/or fountain solution by rotating theplate cylinder and engaging ink and/or fountain solution roller; thedeveloped plate can then directly print images to the receiving sheets(such as paper). Alternatively, the plate can be imagewise exposed withthe laser on a lithographic press, on-press developed on the same presscylinder with ink and/or fountain solution, and then directly printinked images to the receiving sheets.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term yellow-red light means a yellow light, a red light, or anylight with color between yellow and red, such as an orange light; theyellow-red light preferably contains no substantial radiation withwavelengths below a wavelength selected from 400 to 650 nm. Suitableyellow-red light includes a light that is from a fluorescent orincandescent lamp that is covered with a filter that cuts offsubstantially all (preferably all) of the radiation below a wavelengthselected from 400 to 650 nm. Such a cut off wavelength can be 400, 450,500, 550, 600 or 650 nm, or any wavelength between 400 and 650 nm,depending on the spectral sensitivity of the plate. Preferably, theyellow-red light contains no substantial radiation below 450 nm, morepreferably no substantial radiation below 500 nm, and most preferably nosubstantial radiation below 530 nm. Various yellow-red lamps arecommercially available (such as from EncapSulite International Inc. andGeneral Electric), and can be used for the instant invention.

The white light can be a regular fluorescent light, a regularincandescent light, sunlight, any regular office light, or any lightwith broad spectrum over at least the whole visible region (about 380 to750 nm). A white light (such as from an office fluorescent lamp) withaddition of a yellow-red light (such as from a yellow light lamp) isalso considered a white light in this application, because such lighthas broad spectrum over the whole visible region. Preferred white lightis a regular fluorescent light and regular incandescent light, with orwithout addition of sunlight from the windows. More preferred whitelight is a regular fluorescent light.

In this invention, the term “substantial darkness” or “no substantialradiation” means a lighting (including darkness) with lower than 1% ofthe light intensity for all wavelengths for a 100-watt regular tungstenincandescent lamp (also called tungsten lamp or incandescent lamp) at adistance of 2 meters. The term “substantially no radiation below awavelength” means the intensity of the radiation below that wavelengthis lower than 1% of the radiation below that wavelength for a 100-watttungsten lamp at 2 meters. The term “substantial radiation” means thelight intensity is higher than 1% of the radiation for a 100-watttungsten lamp at 2 meters. The term “substantial radiation for certainwavelengths” means the light intensity for such wavelengths is higherthan 1% of a 100-watt tungsten lamp at 2 meters for such wavelengths.The term “substantially light-tight” means that less than 1% of lightcan pass through. The term “substantially all” or “substantially theentire” means at least 99% of all.

The lithographic printing plate of this invention is imagewise exposedwith a laser having a wavelength selected from 200 to 1200 nm, and thenmounted on the plate cylinder of a lithographic press to be developedwith ink and/or fountain solution. At least a portion (by time) of theon-press development is performed with the plate under a yellow-redlight, or under a lighting that contains substantially no radiationbelow a wavelength selected from 400 to 650 nm, or in substantialdarkness. Preferably at least 90% (in terms of time), more preferably atleast 99%, and most preferably all of the on-press development isperformed under a yellow-red light.

After on-press development, the plate directly prints inked images tothe receiving medium (such as paper). At least a portion of suchprinting is under white light or a lighting with substantial radiationbelow a wavelength selected from 400 to 650 nm. Preferably at least aportion (in terms of time), more preferably at least 90%, even morepreferably at least 99%, and most preferably all of the printing isperformed under white light.

The plate can be imagewise exposed with a laser on an imaging device(also called laser imager) off press or on press. For on-press imaging,the plate is preferably mounted on the plate cylinder of the press. Atleast a portion (by time) of the laser exposure is performed with theplate under a yellow-red light, under a lighting that containssubstantially no radiation below a wavelength selected from 400 to 650nm, or in substantial darkness. Preferably at least 90% (in terms oftime), more preferably at least 99%, and most preferably all of theon-press laser exposure is performed under a yellow-red light.

For off-press laser exposure, the exposed plate can be further heated to50 to 200° C. for 1 to 600 seconds, preferably 70 to 150° C. for 1 to300 seconds, to further harden the photosensitive layer in the exposedareas without causing hardening in the non-exposed areas before mountingon press for development with ink and/or fountain solution. The plate ispreferably under a yellow-red light, under a lighting that containssubstantially no radiation below a wavelength selected from 400 to 650nm, or in substantial darkness during at least a portion (in terms oftime), preferably substantially all and more preferably all, of suchheat treatment.

For off-press laser exposure of a plate with a water soluble ordispersible overcoat, the exposed plate can be rinsed with water or anaqueous solution to remove the overcoat without developing thephotosensitive layer before mounting on press for development with inkand/or fountain solution. The plate is preferably under a yellow-redlight, under a lighting that contains substantially no radiation below awavelength selected from 400 to 650 nm, or in substantial darknessduring at least a portion (in terms of time), preferably substantiallyall and more preferably all, of such water rinse.

The lighting that contains substantially no radiation below a wavelengthselected from 400 to 650 nm (usually as a yellow-red light) allows areasonable (although not full) working lighting for the operators duringlaser exposure and/or on-press development without causing hardening ofthe photosensitive layer at least within limited time. Alternatively,the plate can be handled automatically in substantial darkness,including in a substantially dark room, or in a substantiallylight-tight box of any shape such as on an exposure device and/or pressshielded with covers that prevent substantially all room light fromreaching the plate. During the handling before exposure, the plate ispreferably under a yellow-red room light for manual loading, or within asubstantially light-tight cassette or cartridge for automaticallyloading onto the exposure device. For off-press laser exposure, duringthe handling before mounting on press, the exposure device and the pressare preferably under a yellow-red room light.

One or more central switches can be installed on the press, the exposuredevice, the walls of the pressroom, and/or other place in the pressroomto switch the yellow-red light source and white light source. The lightsources are preferably controlled, at least manually and/orelectronically, with at least one controlling center which is capable ofswitching (i) the yellow-red light source on and the white light sourceoff, (ii) the white light source on and the yellow-red light source off,(iii) both the yellow-red light source and white light source off, or(iv) both the yellow-red light source and white light source on. Morepreferably, the light controlling center is capable of switching thelight sources to one of the three statuses: (i) the yellow-red lightsource on and the white light source off, (ii) the white light source onand the yellow-red light source off, (iii) both the yellow-red lightsource and white light source off.

It is noted that a yellow-red light source can consist of one or moreyellow-red light lamps (such as six 40-watt fluorescent lamps withorange covers installed on the pressroom ceiling controlled with aswitch), and a white light source can consist of one or more white lightlamps (such as eight 40-watt regular fluorescent lamps installed on thepressroom ceiling controlled with a switch).

The imager room or pressroom has no or only limited openings to outsideso that no or only limited light enters the pressroom, during theoperations which require that the white light source be turned off. Theopening can be transparent to all light or only transparent to ayellow-red light (such as with yellow-red glass), preferably onlytransparent to yellow-red light. Preferably less than 1% of any light,or of the light with wavelengths below a wavelength selected from 400 to650 nm, enters the pressroom from outside. The imager room or pressroomis in substantial darkness, under a weak yellow-red lighting (such asfrom a yellow-red filtering window), or under a lighting that is atleast 10 times (preferably 100 times) weaker than normal officelighting, more preferably in substantial darkness, when both theyellow-red light source and the white light source are off duringtypical operations of this invention. The lighting of the room (withboth yellow-red and white light sources off) should be sufficiently weak(preferably the room is substantially dark and more preferablycompletely dark) so that it does not cause hardening of thephotosensitive layer of a non-covered plate within at least 30 minutes.Depending on the sensitivity of the plate, the dimness of the room whenboth the yellow-red and white light sources are off can be different.

The imager room or pressroom preferably has one or more closed windowsor shields which are non-transparent and may be opened to allow outsidelight or both outside light and outside air in. Such window or shield isgenerally closed, and may be opened during the lithographic printing orwhen it is safe to turn on the white light source (such as when allnon-developed plates are fully shielded with covers in an imager,cassette, collector, and/or box). The door of the imager room orpressroom is generally closed, and may be opened during the lithographicprinting or when it is safe to turn on the white light source.

The plates can be packaged in a substantially light-tight (or yellow-redlight passing only) cassette (preferably light-tight cassette). Thecassette can be connected to the laser exposure device withsubstantially light-tight (or yellow-red light passing only) covers(preferably light-tight covers) for the plate being exposed. The platecan be automatically transferred to the exposure device for laserexposure. The exposed plate can be transferred to the press for on-pressdevelopment manually under yellow-red light, or automatically underyellow-red light or in substantial darkness. The plate cassette can beany design which can holds one or more plates and can feed out one plateat a time. A light-tight cassette has non-transparent covers to preventthe room light from reaching the plate within the cassette.

The plate on the press before on-press development can be open to theroom lighting that is a yellow-red light or in substantial darkness.Preferably, the press is shielded with covers that allow substantiallyonly yellow-red light passing through or substantially no light passingthrough; this allows white lighting for the pressroom during on-pressdevelopment.

For on-press exposure and development, the plate can be exposed on pressbefore mounting on the plate cylinder (such as exposed with a flatbedlaser scanner installed on press), or can be exposed on the platecylinder. The plate on the press can be open to the room lighting thatis a yellow-red light or in substantial darkness. Preferably, the pressis shielded with covers that prevent substantially all of the radiationbelow a wavelength selected from 400 to 650 nm from reaching the platemounted on the press during exposure and/or on-press development. Theplate can be loaded manually under a yellow-red room light. Preferably,the plate is automatically loaded onto the press for on-press exposureand development from a substantially light-tight cassette, under whiteroom lighting. After on-press development, a portion of the covers canbe opened so that the plate can be viewed under white light duringprinting.

When the plate is handled, imagewise exposed, and/or on-press developedwith ink and/or fountain solution under a yellow-red light or insubstantial darkness (but not complete darkness), the operator can weara pair of night vision goggles or other vision enhancing device so thathe or she can see things more clearly without the requirement of fillwhite light.

In a preferred embodiment of this invention, the laser exposed plate ison-press developed with ink and/or fountain solution, and thenlithographically prints out inked images to the receiving medium (suchas paper) in a pressroom having a yellow-red light source and a whitelight source; the yellow-red light source is on and the white lightsource is off during at least a portion (in terms of time) of theon-press development, and the white light source is on (with theyellow-red light off or on, preferably off) during at least a portion(in terms of time) of the lithographic printing. Preferably, theyellow-red light source is on and the white light source is off duringat least 90%, more preferably at least 99%. and most preferably all (interms of time) of the on-press development, and the white light sourceis on during at least 90%, more preferably at least 99%, and mostpreferably all (in terms of time) of the lithographic printing.Preferably, the pressroom is in substantial darkness when both theyellow-red light source and the white light source are off.

In another preferred embodiment of this invention, both the laserexposure device and the lithographic press are in a pressroom having ayellow-red light source and a white light source; the yellow-red lightsource is on and the white light source is off during at least a portion(in terms of time) of the laser exposure and on-press development, andthe white light source is on (with the yellow-red light off or on,preferably off) during at least a portion (in terms of time) of thelithographic printing. Preferably, the yellow-red light source is on andthe white light source is off during at least 90%, more preferably atleast 99%, and most preferably all (in terms of time) of the laserexposure and on-press development, and the white light source is onduring at least 90%, more preferably at least 99%, and most preferablyall (in terms of time) of the lithographic printing.

In a third preferred embodiment of this invention, the plate isimagewise exposed with a laser on a lithographic press in a pressroomhaving a yellow-red light source and a white light source; theyellow-red light source is on and the white light source is off duringat least a portion (in terms of time) of the laser exposure and on-pressdevelopment, and the white light source is on (with the yellow-red lightoff or on, preferably off) during at least a portion (in terms of time)of the lithographic printing. Preferably, the yellow-red light source ison and the white light source is off during at least 90%, morepreferably at least 99%, and most preferably all (in terms of time) ofthe laser exposure and on-press development, and the white light sourceis on during at least 90%, more preferably at least 99%, and mostpreferably all (in terms of time) of the lithographic printing.

In a fourth preferred embodiment of this invention, the lithographicpress is in a pressroom having a yellow-red light source and a whitelight source; the yellow-red light source is turned on and the whitelight source is turned off at or before the start of the on-pressdevelopment, and the white light source is then turned on (with orwithout the yellow-red light source being turned off) around the end ofon-press development. Preferably, the yellow-red light source is turnedoff when the white light source is turned on.

In a fifth preferred embodiment of this invention, both the exposuredevice and the lithographic press are in a pressroom having a yellow-redlight source and a white light source; the yellow-red light source isturned on and the white light source is turned off at or before thestart of the laser exposure, and the white light source is then turnedon (with or without the yellow-red light source being turned off) aroundthe end of on-press development. Preferably, the yellow-red light sourceis turned off when the white light source is turned on.

In a sixth preferred embodiment of this invention, the lithographicpress is in a pressroom having a yellow-red light source and a whitelight source; the yellow-red light source is on during all theoperations of the press; and the white light source is turned off at orbefore the start of the on-press development, and is then turned onaround the end of on-press development. Preferably, the white lightsource is turned off at or before the start of the laser exposure, ifthe laser exposure is also in the pressroom.

In a seventh preferred embodiment of this invention, the light sourcesare controlled at least from (i) the exposure device which is capable ofautomatically turning off the white light source, if it is on, andturning on the yellow-red light source, if it is off, after setting upand until at least completing a laser exposure job; and (ii) the presswhich is capable of automatically turning on the white light source(with or without turning off the yellow-red light source, preferablywith turning off the yellow light source) after starting the press (torotate the cylinders) for 1 to 600 rotations of the plate cylinder orfor 1 to 600 seconds. If the exposure device has a job in the queue, isexposing a plate, or has an exposed plate on it waiting to be removed,the light switching function of the press will postpone until theexposure device finishes the job and the exposed plate on the exposuredevice has been removed for 0 to 600 seconds. Preferably, the yellow-redlight source is turned on and the white light source is turned off at orbefore the start of on-press development, and the white light source isturned on (with or without the yellow-red light source being turned off,preferably with the yellow-red light source being turned off) at the endof or during on-press development or during lithographic printing, morepreferably around the end of on-press development.

In an eighth preferred embodiment of this invention, the plate isimagewise exposed on a press and then developed with ink and/or fountainsolution on the same press, in a pressroom having a yellow-red lightsource and a white light source; and the light sources are controlled atleast from the press which (i) is capable of automatically turning offthe white light source, if it is on, and turning on the yellow-red lightsource, if it is off, after setting up a laser exposure job and untilcompleting the laser exposure and then engaging the fountain rollerand/or the ink roller to the plate cylinder for 1 to 600 rotations ofthe plate cylinder or for 1 to 600 seconds; and (ii) is capable ofautomatically turning on the white light source (with or without turningoff the yellow-red light source, preferably with turning off theyellow-red light source) after starting the press (to rotate thecylinders) for 1 to 600 rotations of the plate cylinder or for 1 to 600seconds. Preferably, the yellow-red light source is turned on and thewhite light source is turned off at or before the start of on-presslaser exposure (more preferably before mounting the plate on press), andthe white light source is turned on (with or without the yellow-redlight source being turned off, preferably with the yellow-red lightsource being turned off) at the end of or during on-press development orduring lithographic printing, more preferably around the end of on-pressdevelopment.

In a ninth preferred embodiment of this invention, there are one or morepresses and one or more exposure devices in a pressroom; and the lightsources are controlled at least from (i) the exposure devices each ofwhich is capable of automatically turning off the white light source, ifit is on, and turning on the yellow-red light source, if it is off,after setting up and until at least completing a laser exposure job; and(ii) the presses each of which is capable of automatically turning onthe white light source after starting the press for 1 to 600 rotationsof the plate cylinder or for 1 to 600 seconds; wherein if any of theexposure devices has a job in the queue, is exposing a plate, or has anexposed plate on it waiting to be removed, the light switching function(to turn on the white light) of the presses will postpone until theexposure device finishes the job and the exposed plate on the exposuredevice has been removed for 0 to 600 seconds.

In a tenth preferred embodiment of this invention, the plate can beimagewise exposed with a laser on a press, developed with ink and/orfountain solution on the same press, and then lithographically printinked images to the receiving medium (such as paper); wherein the pressis shielded with covers to block off substantially all of the room lightor of the below-450 nm portion of the room light from reaching the platemounted on said press during at least a portion (preferablysubstantially all) of the on-press exposure and development, and atleast a part of said covers is opened during at least a portion(preferably substantially all) of the lithographic printing. The platecan be mounted onto the press for laser exposure, on-press developmentand lithographic printing, manually or automatically, preferablyautomatically from a substantially light-tight cassette or cartridge.

In an eleventh preferred embodiment of this invention, the plate isexposed with a laser while mounted on a lithographic press, and saidpress is connected to a light-tight cassette for feeding the plate toautomatically mount to said press for said imagewise exposure, on-pressdevelopment, and lithographic printing; said press is in a pressroomhaving a yellow-red light source and a white light source; theyellow-red light source is on and the white light source is off duringat least a portion (in terms of time) of the imagewise exposure (step b)and on-press development (step c), and the white light source is on(with the yellow-red light source off or on, preferably off) during atleast a portion of the lithographic printing (step d). Preferably, theyellow-red light source is on and the white light source is off duringat least 90%, more preferably at least 99%, and most preferably all ofsteps (b) and (c), and the white light source is on during at least 90%,more preferably at least 99%, and most preferably all of step (d).Further preferably, the yellow-red light source is turned on and thewhite light source is turned off before mounting the plate on press (astep before step b), and the white light source is then turned on (withor without the yellow-red light source being turned off) around the endof on-press development (step c).

In a twelfth preferred embodiment of this invention, the plate isexposed on a laser imager; said imager is connected to a plate cassettefor feeding the plate to the imager and is also connected to a platecollector for collecting the exposed plate; said imager, cassette andcollector are shielded with covers so that no or substantially no roomlight or the below-450 nm portion of the room light reaches the platewhile the plate is in the cassette, imager or collector, or during thetransportation between cassette, imager or collector; and the exposedplate is picked up from the collector to mount to a lithographic pressfor on-press development and lithographic printing. Here said imager andpress are in a pressroom having a yellow-red light source and a whitelight source; said yellow-red light source is on and said white lightsource is off in said pressroom when a portion of said covers is opened,when the exposed plate is picked up from the collector to mount to saidpress, or during at least a portion (preferably at least 90%, morepreferably at least 99%, most preferably all, by time) of said on-pressdevelopment; and said white light source is on (with the yellow lightsource off or on) during at least a portion (preferably at least 90%,more preferably at least 99%, most preferably all, by time) of saidlithographic printing.

In a thirteenth preferred embodiment of this invention, the plate isexposed on a laser imager in an imager room, the exposed plate is placedin a light-tight box to transport to a pressroom, and the exposed plateis then picked up from said box to mount to a lithographic press foron-press development and lithographic printing. Here said imager is in aroom (imager room) having a yellow-red light source (with or without awhite light source), and said press is in another room (pressroom)having a yellow-red light source and a white light source, saidyellow-red light source in said pressroom is on and said white lightsource in said pressroom is off when the plate is picked up from saidbox to mount to said press, or during at least a portion (preferably atleast 90%, more preferably at least 99%, most preferably all, by time)of said on-press development; and said white light source in saidpressroom is on (with the yellow light off or on) during at least aportion (preferably at least 90%, more preferably at least 99%, mostpreferably all, by time) of the lithographic printing. The light-tightbox can be the plate collector of the imager which can be detached fromthe imager; alternatively, the light-tight box can be a separatelight-tight box where the exposed plate is transferred from the platecollector to the light-tight box, preferably under yellow-red light.

In a fourteenth preferred embodiment of this invention, the plate isexposed on a laser imager in an imager room, the exposed plate istransferred (preferably automatically) through a light-tight passagefrom the imager room into a light-tight box which is located fully orpartially in a pressroom, and the exposed plate is then picked up fromthe box in the pressroom to mount to a lithographic press for on-pressdevelopment and lithographic printing. Here said imager is in a room(imager room) having a yellow-red light source (with or without a whitelight source), and said press is in another room (pressroom) having ayellow-red light source and a white light source; said yellow-red lightsource in said pressroom is on and said white light source in saidpressroom is off when the plate is picked up from the box to mount tosaid press and during at least a portion (preferably at least 90% morepreferably at least 99%, most preferably all, by time) of said on-pressdevelopment; and said white light source in said pressroom is on (withthe yellow light source off or on) during at least a portion (preferablyat least 90%, more preferably at least 99%, most preferably all, bytime) of the lithographic printing.

The lithographic printing plate suitable for the instant inventioncomprises on a substrate a photosensitive layer; wherein saidphotosensitive layer is soluble or dispersible in ink (for waterlessplate) or in ink and/or fountain solution (for wet plate) and capable ofhardening upon exposure to a laser, and at least the hardened areas ofsaid photosensitive layer exhibits an affinity or aversion substantiallyopposite to the affinity or aversion of said substrate to at least oneprinting liquid selected from the group consisting of ink and anadhesive fluid for ink. Here, the photosensitive layer can have the sameaffinity or aversion as the substrate and change to opposite affinity oraversion upon laser exposure, with or without further treatment such ascontacting with ink and/or fountain solution, (with phase change); orcan have opposite affinity or aversion to the substrate both before andafter laser exposure (no phase change). Preferably, said photosensitivelayer exhibits an affinity or aversion substantially opposite to theaffinity or aversion of said substrate (no phase change, includingwaterless plate and wet plate). More preferably, said photosensitivelayer is oleophilic (and hydrophobic) and said substrate is hydrophilic(wet plate). An adhesive fluid for ink is a fluid that repels ink;fountain solution is the most commonly used adhesive fluid for ink. Anink and/or fountain solution soluble or dispersible overcoat can befurther coated on said photosensitive layer.

Usually, as for most printing plates described in the literature, thephotosensitive layer exhibits an affinity or aversion substantiallyopposite to the affinity or aversion of the substrate to at least oneprinting liquid selected from the group consisting of ink and anadhesive fluid for ink (fountain solution is a preferred adhesive fluidfor ink), and does not switch its affinity or aversion upon laserexposure. However, certain photosensitive layer exhibits substantiallythe same affinity or aversion as the substrate and is capable ofswitching to opposite affinity or aversion upon exposure to an actinicradiation (with or without further treatment such as on-pressdevelopment), as described in U.S. Pat. Nos. 6,331,375, 5,910,395,6,720,464, and 6,136,503. Both non-phase-switchable photosensitive layerand phase-switchable photosensitive layer can be used for the currentinvention. Preferred is a non-phase-switchable photosensitive layer(coated on a substrate with opposite affinity or aversion). Morepreferred is an oleophilic photosensitive layer (coated on a hydrophilicsubstrate).

The substrate employed in the lithographic plates of this invention canbe any lithographic support. Such a substrate may be a metal sheet, apolymer film, or a coated paper. Aluminum (including aluminum alloy)sheet is a preferred metal support. Particularly preferred is analuminum support that has been grained and anodized (with or withoutdeposition of a barrier layer). Polyester film is a preferred polymericfilm support. A surface coating may be coated to achieve desired surfaceproperties. For wet plate, the substrate should have a hydrophilic oroleophilic surface, depending on the surface properties of thephotosensitive layer; commonly, a wet lithographic plate has ahydrophilic substrate and an oleophilic photosensitive layer. Forwaterless plate, the substrate should have an oleophilic or oleophobicsurface, depending on the surface properties of the photosensitivelayer.

Particularly suitable hydrophilic substrate for a wet lithographic plateis an aluminum support that has been grained and anodized, such asubstrate is preferably further deposited with a hydrophilic barrierlayer. Surface graining (or roughening) can be achieved by mechanicalgraining or brushing, chemical etching, and/or AC electrochemicalgraining. The roughened surface can be further anodized to form adurable aluminum oxide surface using an acid electrolyte such assulfuric acid and/or phosphoric acid. The roughened and anodizedaluminum surface can be further thermally or electrochemically coatedwith a layer of silicate or hydrophilic polymer such as polyvinylphosphonic acid, polyacrylamide, polyacrylic acid, polybasic organicacid, copolymers of vinyl phosphonic acid and acrylamide to form adurable hydrophilic layer. Polyvinyl phosphonic acid and its copolymersare preferred polymers. Processes for coating a hydrophilic harrierlayer on aluminum in lithographic plate application are well known inthe art, and examples can be found in U.S. Pat. Nos. 2,714,066,4,153,461, 4,399,021, and 5,368,974. Suitable polymer film supports fora wet lithographic plate include a polymer film coated with ahydrophilic layer, preferably a hydrophilic layer that is crosslinked,as described in U.S. Pat. No. 5.922,502.

For preparing lithographic printing plates of the current invention, anyphotosensitive layer is suitable which is capable of hardening uponexposure to a laser having a wavelength selected from 200 to 1200 nm,and is soluble or dispersible in ink and/or fountain solution. Herehardening means becoming insoluble and non-dispersible in ink and/orfountain solution. In this invention, hardening can be achieved throughany means, including chemical reactions (such as polymerization,crosslinking, and chemical changes of monomer, polymer or compound) andphysical changes (such as coalescence of polymer particles). Preferably,hardening is achieved through chemical reaction (such as polymerization,crosslinking, or chemical change). More preferably, hardening isachieved through crosslinking or polymerization of the resins (polymersand/or monomers). Most preferably, hardening is achieved throughpolymerization of the monomers. A laser sensitive dye or pigment isusually used in the photosensitive layer. The photosensitive layerpreferably has a coverage of from 100 to 3000 mg/m², more preferablyfrom 300 to 2000 mg/m², and more preferably from 500 to 1500 mg/m².

Photosensitive layers suitable for the current invention may beformulated from various photosensitive materials, usually with additionof a sensitizing dye or pigment. The composition ratios (such as monomerto polymer ratio) are usually different from conventional platesdesigned for development with a regular liquid developer. Variousadditives may be added to, for example, allow or enhance on-pressdevelopability. Such additives include surfactant, plasticizer, watersoluble polymer or small molecule, and ink soluble polymer or smallmolecule. The addition of nonionic surfactant is especially helpful inmaking the photosensitive layer dispersible with ink and fountainsolution, or emulsion of ink and fountain solution. Various additivesuseful for conventional photosensitive layer can also be used. Theseadditives include pigment, dye, exposure indicator, and stabilizer.

In this application, the term monomer includes both monomer andoligomer, and the term (meth)acrylate includes both acrylate andmethacrylate (A monomer means a monomer or an oligomer, and a(meth)acrylate monomer means an acrylate monomer, a methacrylatemonomer, or a monomer with both acrylate and methacrylate groups.). Theterm “comprises a . . . ” means “comprises at least one . . . ”; forexample, the term “comprising a monomer” means “comprising at least onemonomer.”

Photosensitive materials useful in wet plates of this invention include,for example, photosensitive compositions comprising a polymerizablemonomer, an initiator, a sensitizing dye, and optionally a polymer.

Photosensitive oleophobic materials useful in waterless plates of thisinvention include, for example, compositions comprising a monomer havingperfluoroalkyl or polysiloxane groups and crosslinkable terminal groups,an initiator, and a sensitizing dye.

Infrared laser sensitive (thermosensitive) materials useful for wetlithographic plates of this invention include, for example,thermosensitive compositions comprising a polymerizable monomer, aninitiator, an infrared light absorbing dye, and optionally a polymer.Also useful thermosensitive materials are infrared sensitivecompositions comprising a crosslinkable polymer and an infraredabsorbing dye or pigment. Further useful thermosensitive materials areinfrared sensitive compositions comprising a polymer or compound capableof becoming insoluble upon heat and an infrared absorbing dye orpigment. Yet further useful thermosensitive materials are infraredsensitive compositions comprising a polymeric particulate dispersion andan infrared absorbing dye or pigment.

Visible (including violet) laser sensitive materials useful for wetplates of this invention include, for example, photosensitivecompositions comprising a polymerizable monomer, an initiator, a visiblelight sensitizing dye, and optionally a polymer. Also useful visiblelaser sensitive materials are photosensitive materials comprising acrosslinkable or polymerizable polymeric binder and a visible lasersensitizing dye, preferably with addition of an initiator.

Violet or ultraviolet laser sensitive materials useful as photosensitivelayer of this invention include, for example, photosensitivecompositions comprising a polymerizable monomer, an initiator, a violetor ultraviolet sensitizing dye, and optionally a polymeric binder; ahydrogen donor is preferably added to accelerate the polymerization.Also useful violet or ultraviolet laser sensitive materials arephotosensitive materials comprising a crosslinkable or polymerizablepolymeric binder and a violet or ultraviolet laser sensitizing dye,preferably with addition of an initiator.

Polymeric binder for the photosensitive layer of this invention can beany solid film-forming polymer. Such polymer may or may not have(meth)acrylate groups or other ethylenic groups (such as allyl groups).Examples of suitable polymeric binders include (meth)acrylic polymersand copolymers (such as polybutylmethacrylate, polyethylmethacrylate,polymethylmethacrylate, polymethylacrylate,butylmethacrylate/methylmethacrylate copolymer,methylmethacrylate/methylmethacrylic acid copolymer,polyallylmethacrylate, and allylmethacrylate/methacrylic acidcopolymer), polyvinyl acetate, polyvinyl butyrate, polyvinyl chloride,styrene/acrylonitrile copolymer, styrene/maleic anhydride copolymer andits partial ester, nitrocellulose, cellulose acetate butyrate, celluloseacetate propionate, vinyl chloride/vinyl acetate copolymer,butadiene/acrylonitrile copolymer, polyurethane binder, polymeric binderhaving acetoacetate groups (such as the acetoacetylated polymers asdescribed in U.S. Pat. Nos. 6,919,416 and 7,001,958), and polymericbinder having polymer backbone with recurring units having pendantpoly(alkylene glycol) side chains. The polymeric binder suitable for thephotosensitive layer of this invention has a weight average molecularweight of at least 5,000, preferably from 10,000 to 1,000,000, morepreferably from 20,000 to 500,000, and most preferably from 50,000 to200,000 Dalton. It is noted that polymeric compounds with weight averagemolecular weight of less that 5,000 can also be added in thephotosensitive layer of this invention; however, in order to avoidconfusion, such compounds are not considered as polymeric binder and arecalled oligomer (without or with polymerizable groups) in thisapplication (oligomers having polymerizable groups are also included inthe definition of monomers in this application).

Suitable free-radical polymerizable monomers include any monomer oroligomer with at least one ethylenically unsaturated group. Suchmonomers include monofunctional, difunctional, and multifunctional(meth)acrylate monomers or oligomers, such as (meth)acrylate esters ofethylene glycol, trimethylolpropane; pentaerythritol, ethoxylatedethylene glycol and ethoxylated trimethylolpropane; multifunctionalurethanated (meth)acrylate; epoxylated (meth)acrylate; oligomeric amine(meth)acrylate: and phosphate ester-containing (meth)acrylate (such asphosphate ester of 2-hydroxyethyl methacrylate, and various phosphateester containing (meth)acrylate monomers as described in U.S. Pat. Nos.4,101,326, 5,679,485, 5,776,655 and 7,316,887, and U.S. Pat. App. No.2008/0008957). The monomers can be urethane (meth)acrylate, ornon-urethane (meth)acrylate. Combination of both urethane (meth)acrylateand non-urethane (meth)acrylate monomers can be used. The monomerspreferably has at least 3 (meth)acrylate groups, more preferably atleast 4 (meth)acrylate groups, even more preferably at least 5(meth)acrylate groups, and most preferably at least 6 (meth)acrylategroups. However, monofunctional or difunctional (meth)acrylate monomercan be added into the photosensitive layer having multifunctional(meth)acrylate monomers; the total amount of such monofunctional ordifunctional monomers is preferably less than 50% by weight of the totalmonomers, more preferably less than 30%, and most preferably less than10%. Acrylate monomer is preferred over methacrylate monomer because ofthe faster photospeed of acrylate group over methacrylate group. Themonomer has a molecular weight of less than 5,000, preferably from 100to 3,000, more preferably from 200 to 2,000, and most preferably from300 to 1,500 Dalton.

Urethane (meth)acrylate monomers include any compounds having at leastone urethane linkage (—NHCOO—) and at least one (meth)acrylate group.Preferred urethane (metha)acrylate monomers are those with at least 3(meth)acrylate groups, more preferably at least 4 (meth)acrylate groups,even more preferably at least 5 (meth)acrylate groups, and mostpreferably at least 6 (meth)acrylate groups. Urethane (meth)acrylatemonomer is usually formed by reacting a compound having at least oneisocyanate group with a (meth)acrylate compound having a hydroxy group.Urethane monomer with 2 or more (meth)acrylate groups are usually formedfrom a compound having one or more isocyanate groups and a(meth)acrylate compound having a hydroxy group and one or more(meth)acrylate groups. For example, a tetrafunctional urethane(meth)acrylate monomer can be formed from a compound having one hydroxygroup and 2 (meth)acrylate groups with a bifunctional isocyanatecompound. Suitable isocyanate compounds include, for example, aromaticdiisocyanate such as p-phenylene diisocyanate. 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, 4,4′-diphenylmethanediisocyanate, naphthalene-1,5-diisocyanate and tolydine diisocyanate;aliphatic diisocyanate such as hexamethylene diisocyanate, lysinemethylester diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate and dimeracid diisocyanate; alicyclic diisocyanate such as isophoronediisocyanate, and 4,4′-methylenebis(cyclohexylisocyanate); aliphaticdiisocyanate having an aromatic ring, such as xylylene diisocyanate;triisocyanate such as lysine ester triisocyanate. 1,6,11-undecanetriisocyanate, 1,8-diisocyanate-4-isocyanatemethyloctane,1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate,tris(isocyanate phenylmethane) and tris(isocyanatephenyl)thiophosphate;and polyisocyanate formed from condensation of three or morediisocyanate compounds such as 2,4-tolylene diisocyanate isocyanuratetrimer, 2,4-tolylene diisocyanate-trimethylolpropane adduct,1,6-hexanediisocyante isocyanurate trimer. Suitable (meth)acrylatecompounds with one hydroxy group include pentaerythritoltri(meth)acrylate, dipentaerythritol penta(meth)acrylate,ditrimethylolpropane tri(meth)acrylate and pentaerythritoldi(meth)acrylate monostearate. Various urethane (meth)acrylate monomersare described in U.S. Pat. No. 6,232,038 and U.S. Pat. Pub. No.2002/0018962, and can be used as the urethane (meth)acrylate monomers ofthis instant invention. Among the urethane (meth)acrylate monomers,urethane acrylate monomer is preferred. Either aromatic urethane(meth)acrylate monomer (which contains at least one aromatic group inthe molecule) or aliphatic urethane (meth)acrylate monomer (which doesnot contain any aromatic group in the molecule) or both can be used in aphotosensitive layer of this invention.

Suitable non-urethane (meth)acrylate monomers can be any (meth)acrylatemonomers without urethane linkage (—NHCOO—) in the molecule. Suitablenon-urethane (meth)acrylate monomers include, for example,trimethylolpropane triacrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate, dipentaerythritolhexa(meth)acrylate, di(trimethylolpropane)tetra(meth)acrylate. Among thenon-urethane (meth)acrylate monomers, non-urethane acrylate monomer ispreferred.

The free radical initiators useful for the photosensitive layer of thisinvention include any initiators capable of generating free radicals orother activating species to cause polymerization of the monomers uponexposure to a laser having a wavelength selected from 200 to 1200 nm,with or without the presence of a sensitizing dye. Suitable free-radicalinitiators include, for example, onium salts such as diaryliodoniumhexafluoroantimonate, diaryliodonium hexafluorophosphate, diaryliodoniumtriflate, (4-(2-hydroxytetradecyl-oxy)phenyl)phenyliodoniumhexafluoroantimonate. (4-octoxyphenyl)phenyliodoniumhexafluoroantimonate, bis(4-t-butylphenyl)iodonium hexafluorophosphate,triarylsulfonium hexafluorophosphate, triarylsulfoniump-toluenesulfonate, (3-phenylpropan-2-onyl)triaryl phosphoniumhexafluoroantimonate and N-ethoxy(2-methyl)pyridiniumhexafluorophosphate, and the onium salts as described in U.S. Pat. Nos.5,955,238, 6,037,098 and 5,629,354; borate salts such astetrabutylammonium triphenyl(n-butyl)borate, tetraethylammoniumbiphenyl(n-butyl)borate, diphenyliodonium tetraphenylborate, andtriphenylsulfonium triphenyl(n-butyl)borate, and the borate salts asdescribed in U.S. Pat. Nos. 6,232,038 and 6,218,076; haloalkylsubstituted s-triazines such as2,4-bis(trichloromethyl)-6-(p-methoxy-styryl)-s-triazine,2,4-bis(trichloromethyl)-6-(4-methoxy-naphth-1-yl)-s-triazine,2,4-bis(trichloromethyl)-6-piperonyl-s-triazine, and2,4-bis(trichloromethyl)-6-[(4-ethoxyethylenoxy)-phen-1-yl]-s-triazine,and the s-triazines as described in U.S. Pat. Nos. 5,955,238, 6,037,098,6,010,824, and 5,629,354; hexaarylbiimidazole compounds such as2,2′-bis(2-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole,2,2′-bis(2-ethoxyphenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole,2,2′,4-tris(2-chlorophenyl)-5-(3,4-dimethoxyphenyl)-4′,5′-diphenyl-1,1′-biimidazole,and 2-(1-naphthyl)-4,5-diphenyl-1,2′-biimidazole; and titanocenecompounds such asbis(η⁹-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium.For thermosensitive plate, onium salts, borate salts, and s-triazinesare preferred free radical initiators; onium sails and borate salts aremore preferred; and onium salts (particularly diaryliodonium salts andtriarylsulfonium salts) are most preferred. For violet or ultravioletplate, hexaarylbiimidazole compounds and titanocene compounds arepreferred free radical initiators, and hexaarylbiimidazole compounds aremore preferred. One or more initiators can be added in a photosensitivelayer. The initiator is added in the photosensitive layer preferably at0.5 to 40% by weight of the photosensitive layer, more preferably at 2to 30%, and most preferably at 5 to 20%.

Suitable polyfunctional epoxy monomers include, for example,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate,bis-(3,4-epoxycyclohexylmethyl)adipate, difunctional bisphenolA/epichlorohydrin epoxy resin and multifunctionalepichlorohydrin/tetraphenylol ethane epoxy resin.

Suitable cationic initiators include, for example, triarylsulfoniumhexafluoroantimonate, triarylsulfonium hexafluorophosphate,diaryliodonium hexafluoroantimonate, and haloalkyl substituteds-triazine. It is noted that most cationic initiators are also freeradical initiators because, in addition to generating Bronsted acid,they also generate free radicals during photo or thermal decomposition.

Suitable sensitizing dyes in this invention include any compoundscapable of absorbing an imaging radiation and transferring the absorbedradiation energy to the initiator or other component in thephotosensitive layer to cause hardening of the photosensitive layer.Suitable sensitizing dyes include infrared sensitizing dyes (also calledinfrared absorbing dyes), visible sensitizing dyes (including violetsensitizing dyes), and ultraviolet sensitizing dyes. Preferred areinfrared absorbing dyes and violet or ultraviolet sensitizing dyes. Morepreferred are infrared laser absorbing dyes and violet or ultravioletlaser sensitizing dyes.

Infrared absorbers useful in the thermosensitive layer of this inventioninclude any infrared absorbing dye or pigment effectively absorbing aninfrared radiation having a wavelength of 700 to 1,500 nm. It ispreferable that the dye or pigment having an absorption maximum betweenthe wavelengths of 750 and 1,200 nm. Various infrared absorbing dyes orpigments are described in U.S. Pat. Nos. 5,858,604, 5,922,502,6,027,668, 5,705,309, 6,017,677, and 5,677,106, and in the book entitled“Infrared Absorbing Dyes” edited by Masaru Matsuoka, Plenum Press, NewYork (1990), and can be used in the thermosensitive layer of thisinvention. Examples of useful infrared absorbing dyes includesquarylium, croconate, cyanine (including polymethine), phthalocyanine(including naphthalocyanine), merocyanine, chalcogenopyryloarylidene,oxyindolizine, quinoid, indolizine, pyrylium and metal dithiolene dyes.Cyanine and phthalocyanine dyes are preferred infrared absorbing dyes.Examples of useful infrared absorbing pigments include black pigments,metal powder pigments, phthalocyanine pigments, and carbon black. Carbonblack is a preferred infrared absorbing pigment. Mixtures of dyes,pigments, or both can also be used. Infrared absorbing dye is preferredover infrared absorbing pigment because infrared absorbing dye usuallyhas higher absorbing efficiency, gives less visible color, and allowsmolecular level charge or energy transfer to activate the initiator. Theinfrared dye or pigment is added in the thermosensitive layer preferablyat 0.01 to 20% by weight of the thermosensitive layer, more preferablyat 0.1 to 10%, and most preferably at 0.5 to 5%.

Visible or ultraviolet sensitizing dyes useful in the visible orultraviolet sensitive photosensitive layer of this invention include anydyes having a wavelength maximum of from 200 to 600 nm and capable ofdirectly or indirectly causing polymerization of the monomers uponexposure to the corresponding laser. Usually, the visible or ultravioletdye activates an initiator to cause the polymerization of the monomerupon exposure to a laser. Suitable visible and ultraviolet sensitivedyes include, for example, cyanine dyes (including polymethine dyes);rhodamine compounds such as rhodamine 6G perchloride; chromanonecompounds such as 4-diethylaminobenzilidene chromanone;dialkylaminobenzene compounds such as ethyl 4-dimethylaminobenzoate anddialkylaminobenzene; dialkylaminobenzophenone compounds such as4,4′-bis(dimethylamino)benzophenone, 4,4′-bis(diethylamino)benzophenone,2-(p-dimethylaminophenyl)benzooxazole,2-p-diethylaminophenyl)benzooxazole,2-(p-dimethylaminophenyl)benzo[4,5]benzooxazole,2-(p-dimethylaminophenyl)benzo[6,7]benzooxazole,2,5-bis(p-diethylaminophenyl) 1,3,4-oxazole,2-(p-dimethylaminophenyl)benzothiazole,2-(p-diethylaminophenyl)benzothiazole,2-(p-dimethylaminophenyl)benzimidazole,2-(p-diethylaminophenyl)benzimidazole,2,5-bis(p-diethylaminophenyl)1,3,4-thiadiazole,(p-dimethylaminophenyl)pyridine, (p-diethylaminophenyl)pyridine,2-(p-dimethylaminophenyl)quinoline, 2-(p-diethylaminophenyl)quinoline,2-(p-dimethylaminophenyl)pyrimidine or2-(p-diethylaminophenyl)pyrimidine; unsaturated cyclopentanone compoundssuch as2,5-bis{[4-(diethylamino)phenyl]methylene}-(2E,5E)-(9Cl)-cyclopentanoneand bis(methylindolenyl)cyclopentanone; coumarin compounds such as3-benzoyl-7-methoxy coumarin and 7-methoxy coumarin; and thioxanthenecompounds such as 2-isopropylthioxanthenone. Dialkylaminobenzenecompounds and bis(dialkylamino)benzophenone compounds are particularlysuitable for ultraviolet laser sensitive plate.Bis(dialkylamino)benzophenone compounds are particularly suitable forviolet laser sensitive plate. The sensitizing dyes as described in U.S.Pat. Nos. 5,422,204 and 6,689,537, and U.S. Pat. App. Pub. No.2003/0186165 can be used for the photosensitive layer of this invention.The visible or ultraviolet sensitizing dye is added in thephotosensitive layer preferably at 0.1 to 20% by weight of thephotosensitive layer, more preferably 0.5 to 15%, and most preferably 1to 10%.

The photosensitive layer of the present invention may contain one ormore hydrogen donors as a polymerization accelerator. Examples of thehydrogen donors include compounds having a mercapto group (also calledmercapto compounds) such as 2-mercaptobenzothiazole,2-mercaptobenzimidazole, 2-mercaptobenzoxazole and3-mercapto-1,2,4-triazole; and N-aryl-α-amino acids, their salts andesters such as N-phenylglycine, salts of N-phenylglycine, and alkylesters of N-phenylglycine such as N-phenylglycine ethyl ester andN-phenylglycine benzyl ester. Preferred hydrogen donors are mercaptocompounds (more preferably 2-mercaptobenzothiazole,2-mercaptobenzimidazole, 2-mercaptobenzoxazole, and3-mercapto-1,2,4-triazole) and N-aryl-α-amino acids and theirderivatives (more preferably N-phenylglycine, N-phenylglycine ethylester, and N-phenylglycine benzyl ester), most preferred hydrogen donorsare mercapto compounds. Combination of at least one mercapto compoundand at least one N-aryl-α-amino acid or its ester or salt can beadvantageously used in the photosensitive layer to increase thephotospeed. The hydrogen donor is added in the photosensitive layerpreferably at 0.01 to 15% by weight of the photosensitive layer, morepreferably 0.1 to 10%, and most preferably 0.5 to 5%.

Various surfactants can be added into the photosensitive layer to allowor enhance the on-press developability with ink and/or fountain. Bothpolymeric and small molecule surfactants can be used. However, it ispreferred that the surfactant has low or no volatility so that it willnot evaporate from the photosensitive layer of the plate during storageand handling. Nonionic surfactants are preferred. Preferred nonionicsurfactants are polymers and oligomers containing one or more polyether(such as polyethylene glycol, polypropylene glycol, and copolymer ofethylene glycol and propylene glycol) segments. Examples of preferrednonionic surfactants are block copolymers of propylene glycol andethylene glycol (also called block copolymer of propylene oxide andethylene oxide); ethoxylated or propoxylated acrylate oligomers; andpolyethoxylated alkylphenols and polyethoxylated fatty alcohols. Thenonionic surfactant is preferably added at from 0.1 to 30% by weight ofthe photosensitive layer, more preferably from 0.5 to 20%, and mostpreferably from 1 to 10%.

A hydrophilic or oleophilic micro particles can be added into thephotosensitive layer to enhance, for example, the developability andnon-tackiness of the plate. Suitable micro particles include polymerparticles, talc, titanium dioxide, barium sulfate, silicone oxide, andaluminum micro particles, with an average particle size of less than 10microns, preferably less than 5 microns, more preferably less than 2microns, and most preferably less than 1 microns. A suitable particulardispersion is described in U.S. Pat. No. 6,071,675, the entiredisclosure of which is hereby incorporated by reference.

For plates with rough and/or porous surface, a thin releasableinterlayer can be deposited between the substrate and the photosensitivelayer. Preferably, the substrate surface is rough and/or porous enoughand the interlayer is thin enough to allow bonding between thephotosensitive layer and the substrate through mechanical interlocking.Such a plate configuration is described in U.S. Pat. No. 6,014,929, theentire disclosure of which is hereby incorporated by reference.Preferred releasable interlayer comprises a water-soluble polymer.Polyvinyl alcohol (including various water-soluble derivatives ofpolyvinyl alcohol) is the preferred water-soluble polymer. Usually purewater-soluble polymer is coated. However, one or more surfactant andother additives may be added. The water-soluble polymer is generallycoated from an aqueous solution with water as the only solvent. Awater-soluble organic solvent, preferably an alcohol such as ethanol orisopropanol, can be added into the water-soluble polymer aqueous coatingsolution to improve the coatability. The alcohol is preferably added atless than 40% by weight of the solution, more preferably at less than20%, and most preferably at less than 10%. The releasable interlayerpreferably has an average coverage of 1 to 200 mg/m², more preferably 2to 100 mg/m², and most preferably 4 to 40 mg/m². The substratepreferably has an average surface roughness Ra of 0.2 to 2.0 microns,and more preferably 0.4 to 1.0 microns.

The photosensitive layer can be conformally coated onto a roughenedsubstrate (for example, with Ra of larger than 0.4 microns) at thincoverage (for example, of less than 1.2 g/m²) so that the plate can havemicroscopic peaks and valleys on the photosensitive layer coated surfaceand exhibit low tackiness and good block resistance, as described inU.S. Pat. No. 6,242,156, the entire disclosure of which is herebyincorporated by reference.

An ink and/or fountain solution soluble or dispersible overcoat can becoated on the photosensitive layer for the plate of this invention to,for example, improve the photospeed, surface durability, and/or on-pressdevelopability. Particularly preferred overcoat is a water soluble ordispersible overcoat. The overcoat preferably comprises a water-solublepolymer, such as polyvinyl alcohol (including various water-solublederivatives of polyvinyl alcohol). Combination of two or morewater-soluble polymers (such as a combination of polyvinyl alcohol andpolyvinylpyrrolidone) can also be used. Polyvinyl alcohol is a preferredwater-soluble polymer. Various additives, such as surfactant, wettingagent, defoamer, leveling agent and dispersing agent, can be added intothe overcoat formulation to facilitate, for example, the coating ordevelopment process. Examples of surfactants useful in the overcoat ofthis invention include polyethylene glycol, polypropylene glycol, andcopolymer of ethylene glycol and propylene glycol, polysiloxanesurfactants, perfluorocarbon surfactants, alkylphenyl ethylene oxidecondensate, sodium dioctylsulfosuccinate, sodiumdodecylbenzenesulfonate, and ammonium laurylsulfate. Various organic orinorganic emulsion or dispersion may be added into the overcoat to, forexample, reduce the tackiness or moisture sensitivity of the plate. Theovercoat preferably has a coverage of from 0.001 to 3.0 g/m², morepreferably from 0.005 to 1.0 g/m², and most preferably from 0.01 to 0.15g/m².

A preferred thermosensitive lithographic plate of this inventioncomprises on a substrate a thermosensitive layer comprising a polymericbinder, a free radical polymerizable monomer having at least oneterminal ethylenic group, a free-radical initiator, and an infraredabsorbing dye. A nonionic surfactant is preferably added in thethermosensitive layer. Other additives such as surfactant, dye orpigment, exposure-indicating dye (such as leuco crystal violet,leucomalachite green, azobenzene, 4-phenylazodiphenylamine, andmethylene blue dyes), and free-radical stabilizer (such asmethoxyhydroquinone) may be added. The monomer preferably has at least 3(meth)acrylate groups, more preferably at least 4 (meth)acrylate groups,even more preferably at least 5 (meth)acrylate groups, and mostpreferably at least 6 (meth)acrylate groups. The monomer can be aurethane (meth)acrylate monomer or a non-urethane (meth)acrylatemonomer; preferably the monomer is a urethane (meth)acrylate monomer;more preferably both a non-urethane (meth)acrylate monomer and aurethane (meth)acrylate monomer are used in the photosensitive layer.One or more other monomers can be added in the photosensitive layer. Theweight ratio of all the monomers to all the polymeric binders ispreferably larger than 0.5, more preferably larger than 1.0, even morepreferably larger than 1.5, and most preferably larger than 2.0. An inkand/or fountain solution soluble or dispersible overcoat is preferablycoated on the photosensitive layer.

Another preferred thermosensitive lithographic plate of this inventioncomprises on a substrate a thermosensitive layer comprising a polymericbinder, a urethane monomer having at least 3 (meth)acrylate groups, anon-urethane monomer having at least 3 (meth)acrylate groups, afree-radical initiator, and an infrared absorbing dye. Preferably, theurethane monomer has at least 4 (meth)acrylate groups, and thenon-urethane monomer has at least 4 (meth)acrylate groups. Morepreferably, the urethane monomer has at least 6 (meth)acrylate groups. Anonionic surfactant is preferably added. One or more other monomers canbe added in the photosensitive layer. The weight ratio of all theurethane (meth)acrylate monomer to all the non-urethane (meth)acrylatemonomer is preferably from 0.10 to 10.0, more preferably 0.30 to 1.0. Anink and/or fountain solution soluble or dispersible overcoat ispreferably coated on the photosensitive layer.

A third preferred thermosensitive lithographic plate of this inventioncomprises on a substrate a thermosensitive layer comprising a polymericbinder having polymer backbone with recurring units having pendantpoly(alkylene glycol) side chains, a (meth)acrylate monomer having atleast one (meth)acrylate group, a free-radical initiator, and aninfrared absorbing dye. A mercapto group-containing compound ispreferably added. The weight ratio of all the monomers to all thepolymeric binders is preferably at least 1.0, more preferably from 1.5to 6.0, and most preferably from 2.0 to 5.0. An ink and/or fountainsolution soluble or dispersible overcoat is preferably coated on thephotosensitive layer.

A fourth preferred thermosensitive lithographic plate of this inventioncomprises on a substrate a thermosensitive layer comprising a polymericbinder, a urethane (meth)acrylate monomer having at least 4(meth)acrylate groups, a phosphate ester-containing (meth)acrylatemonomer, a free-radical initiator, and an infrared absorbing dye. Amercapto group-containing compound is preferably added. The weight ratioof all the monomers to all the polymeric binders is preferably at least1.0, more preferably from 1.5 to 6.0, and most preferably from 2.0 to5.0. An ink and/or fountain solution soluble or dispersible overcoat ispreferably coated on the photosensitive layer.

A fifth preferred thermosensitive lithographic plate of this inventioncomprises on a substrate a thermosensitive layer comprising an epoxy orvinyl ether monomer having at least one epoxy or vinyl ether group, aBronsted acid generator capable of generating free acid in the presenceof an infrared absorbing dye or pigment upon exposure to an infraredradiation, and an infrared absorbing dye or pigment (preferably infraredabsorbing dye). A polymeric binder is preferably added. Other additivessuch as surfactant, dye or pigment, exposure-indicating dye, and acidquencher (usually an alkaline compound, such as tetrabutylammoniumhydroxide or triethylamine) may be added.

A sixth preferred thermosensitive lithographic plate of this inventioncomprises on a substrate a thermosensitive layer comprising a polymericbinder and an infrared absorbing dye or pigment (preferably infraredabsorbing dye); said thermosensitive layer is developable with inkand/or fountain solution and capable of hardening through crosslinkingof the polymeric binder upon exposure to an infrared laser. A nonionicsurfactant and/or a water-soluble polymer are preferably added in thethermosensitive layer. Other additives such as other surfactant, dye orpigment, and exposure indicating dye can also be added.

A seventh preferred thermosensitive lithographic plate of this inventioncomprises on a substrate a thermosensitive layer comprising a polymericparticles dispersion and an infrared absorbing dye or pigment(preferably infrared absorbing dye); said thermosensitive layer isdevelopable with ink and/or fountain solution and capable of hardeningthrough coalescence of the polymer particles upon exposure to aninfrared laser. A nonionic surfactant and/or a water-soluble polymer arepreferably added in the thermosensitive layer. Other additives such asother surfactant, dye or pigment, and exposure indicating dye can alsobe added.

A preferred visible light sensitive lithographic printing plate of thisinvention comprises on a substrate a photosensitive layer comprising apolymeric binder (with or without ethylenic groups), a free radicalpolymerizable monomer having at least one terminal ethylenic group, afree-radical initiator, and a visible sensitizing dye. A nonionicsurfactant is preferably added in the photosensitive layer. Otheradditives such as surfactant, dye or pigment, exposure-indicating dye,and free-radical stabilizer may be added. The monomer preferably has atleast 3 (meth)acrylate groups, more preferably at least 4 (meth)acrylategroups, even more preferably at least 5 (meth)acrylate groups, and mostpreferably at least 6 (meth)acrylate groups. The monomer can be aurethane (meth)acrylate monomer or a non-urethane (meth)acrylatemonomer; preferably the monomer is a urethane (meth)acrylate monomer;more preferably both a non-urethane (meth)acrylate monomer and aurethane (meth)acrylate monomer are used in the photosensitive layer.One or more other monomers can be added in the photosensitive layer. Theweight ratio of all the monomers to all the polymeric binders ispreferably larger than 0.5, more preferably larger than 1.0, even morepreferably larger than 1.5, and most preferably larger than 2.0. An inkand/or fountain solution soluble or dispersible overcoat is preferablycoated on the photosensitive layer.

A preferred violet or ultraviolet light sensitive lithographic plate ofthis invention comprises on a substrate a photosensitive layercomprising a polymeric binder, a free radical polymerizable monomerhaving at least one terminal ethylenic group, a free-radical initiator,and a violet or ultraviolet sensitizing dye. A hydrogen donor ispreferably added to increase the photospeed; a preferred hydrogen donoris a mercapto group-containing compound. A nonionic surfactant ispreferably added to enhance on-press developability. Other additivessuch as surfactant, dye or pigment, exposure-indicating dye, andfree-radical stabilizer may be added. The monomer preferably has atleast 3 (meth)acrylate groups, more preferably at least 4 (meth)acrylategroups, even more preferably at least 5 (meth)acrylate groups, and mostpreferably at least 6 (meth)acrylate groups. The monomer can be aurethane (meth)acrylate monomer or a non-urethane (meth)acrylatemonomer: preferably the monomer is a urethane (meth)acrylate monomer;more preferably both a non-urethane (meth)acrylate monomer and aurethane (meth)acrylate monomer are used in the photosensitive layer.One or more other monomers can be added in the photosensitive layer. Theweight ratio of all the monomers to all the polymeric binders ispreferably larger than 0.5, more preferably larger than 1.0, even morepreferably larger than 1.5, and most preferably larger than 2.0. An inkand/or fountain solution soluble or dispersible overcoat is preferablycoated on the photosensitive layer.

Another preferred violet or ultraviolet laser sensitive lithographicplate of this invention comprises on a substrate a photosensitive layercomprising a polymeric binder, a monomer having at least 3(meth)acrylate group, a hexaarylbiimidazole or titanocene compound, adialkylaminobenzophenone compound, and a hydrogen donor. Ahexaarylbiimidazole compound is preferred among hexaarylbiimidazole andtitanocene compounds. A preferred dialkylaminobenzophenone compound is a4,4′-bis(dialkylamino)benzophenone compound. A preferred hydrogen donoris a mercapto group-containing compound. Said monomer is preferably aurethane (meth)acrylate monomer. More preferably, said monomer is aurethane (meth)acrylate monomer and said photosensitive layer furthercomprises a non-urethane (meth)acrylate monomer. Even more preferably,said photosensitive layer comprises a urethane monomer with at least 3(meth)acrylate groups and a non-urethane monomer with at least 3(meth)acrylate groups. Most preferably, said photosensitive layercomprises a urethane monomer with at least 4 (meth)acrylate groups and anon-urethane monomer with at least 4 (meth)acrylate groups. A nonionicsurfactant is preferably added in the photosensitive layer. The weightratio of all the monomers to all the polymeric binders is preferablylarger than 0.5, more preferably larger than 1.0, even more preferablylarger than 1.5, and most preferably larger than 2.0. An ink and/orfountain solution soluble or dispersible overcoat is preferably coatedon the photosensitive layer.

A third preferred violet or ultraviolet laser sensitive lithographicplate of this invention comprises on a substrate a photosensitive layercomprising a polymeric binder, a urethane monomer having at least 4(meth)acrylate groups, a hexaarylbiimidazole or titanocene compound, anda dialkylaminobenzophenone compound. A mercapto group-containingcompound is preferably added. The weight ratio of all the monomers toall the polymeric binders is preferably at least 0.5, more preferablyfrom 1.0 to 6.0, and most preferably from 2.0 to 5.0. Ahexaarylbiimidazole compound is preferred among hexaarylbiimidazole andtitanocene compounds. A preferred dialkylaminobenzophenone compound is a4,4′-bis(dialkylamino)benzophenone compound. A non-urethane(meth)acrylate monomer is preferably added. An ink and/or fountainsolution soluble or dispersible overcoat is preferably coated on thephotosensitive layer.

A fourth preferred violet or ultraviolet laser sensitive lithographicplate of this invention comprises on a substrate a photosensitive layercomprising a polymeric binder, a urethane monomer having at least 4(meth)acrylate groups, a non-urethane monomer having at least 4(meth)acrylate groups, a free radical initiator, and a violet orultraviolet sensitizing dye. A mercapto group-containing compound ispreferably added. The weight ratio of the urethane (meth)acrylatemonomer to the non-urethane (meth)acrylate monomer is preferably from0.10 to 10.0, more preferably from 0.20 to 5.0, and most preferably from0.30 to 3.0. The weight ratio of all the monomers to all the polymericbinders is preferably at least 0.5, more preferably from 1.0 to 6.0,even more preferably from 1.5 to 5.0, and most preferably from 2.0 to4.0. A preferred free radical initiator is a hexaarylbiimidazole ortitanocene compound, more preferably a hexaarylbiimidazole compound. Apreferred sensitizing dye is a dialkylaminobenzophenone compound, morepreferably a 4,4′-bis(dialkylamino)benzophenone compound. An ink and/orfountain solution soluble or dispersible overcoat is preferably coatedon the photosensitive layer.

A fifth preferred violet or ultraviolet laser sensitive lithographicplate of this invention comprises on a substrate a photosensitive layercomprising a polymeric binder having polymer backbone with recurringunits having pendant poly(alkylene glycol) side chains, a (meth)acrylatemonomer having at least one (meth)acrylate group, a free-radicalinitiator, and a violet or ultraviolet sensitizing dye. A mercaptogroup-containing compound is preferably added. Other additives such assurfactant, dye or pigment, exposure-indicating dye, and free-radicalstabilizer may be added. The weight ratio of all the monomers to all thepolymeric binders is preferably at least 1.0, more preferably from 1.5to 6.0, and most preferably from 2.0 to 5.0. An ink and/or fountainsolution soluble or dispersible overcoat is preferably coated on thephotosensitive layer.

A sixth preferred violet or ultraviolet laser sensitive lithographicplate of this invention comprises on a substrate a photosensitive layercomprising a polymeric binder, a urethane monomer having at least 4(meth)acrylate groups, a phosphate ester-containing (meth)acrylatemonomer, a free radical initiator, and a violet or ultravioletsensitizing dye. A mercapto group-containing compound is preferablyadded. The weight ratio of all the monomers to all the polymeric bindersis preferably at least 0.5, more preferably from 1.0 to 6.0, and mostpreferably from 2.0 to 5.0. A preferred free radical initiator is ahexaarylbiimidazole or titanocene compound, more preferably ahexaarylbiimidazole compound. A preferred sensitizing dye is adialkylaminobenzophenone compound, more preferably a4,4′-bis(dialkylamino)benzophenone compound. A phosphate-freenon-urethane (meth)acrylate monomer can be added. An ink and/or fountainsolution soluble or dispersible overcoat is preferably coated on thephotosensitive layer.

As for all the photosensitive layer of this invention, the abovephotosensitive layers (including thermosensitive layers) are soluble ordispersible in ink and/or fountain solution, so that they can beon-press developed with ink and/or fountain solution.

On-press developable lithographic plates and photosensitive layers asdescribed in U.S. Pat. Nos. 6,482,571, 6,576,401, 5,548,222, 6,541,183,6,551,757, 6,899,994 and 6,949,327, and U.S. patent application Ser.Nos. 11/057,663, 11/175,518, 11/266,817, 11/336,132, 11,356,911, and11/645,376, the entire disclosures of which are hereby incorporated byreference, can be used for the instant invention.

Infrared lasers useful for the imagewise exposure of the thermosensitiveplates of this invention include laser sources emitting in the nearinfrared region, i.e. emitting in the wavelength range of from 750 to1200 nm, and preferably from 800 to 1100 nm. Particularly preferredinfrared laser sources are laser diodes emitting around 830 nm or aNdYAG laser emitting around 1060 nm. The plate is exposed at a laserdosage that is sufficient to cause hardening in the exposed areas butnot high enough to cause substantial thermal ablation. The exposuredosage is preferably from 1 to 2000 mJ/cm², more preferably from 5 to500 mJ/cm², and most preferably from 20 to 200 mJ/cm², depending on thesensitivity of the thermosensitive layer.

Visible lasers (including violet laser) useful for the imagewiseexposure of the visible light sensitive plates of this invention includeany laser emitting in the wavelength range of from 390 to 600 nm.Examples of suitable visible lasers include frequency-doubled Nd/YAGlaser (about 532 nm), argon ion laser (about 488 nm), violet diode laser(about 405 nm), and visible LEDs. Violet laser diode is especiallyuseful because of its small size and relatively low cost. The exposuredosage is preferably from 1 to 2000 μJ/cm² (0.001 to 2 mJ/cm²) morepreferably from 5 to 500 μJ/cm², and most preferably from 20 to 200μJ/cm², depending on the sensitivity of the photosensitive layer.

Violet or ultraviolet lasers useful for the imagewise exposure of theplates of this invention include any lasers having a wavelength of from200 to 430 nm, such as violet laser diodes having a wavelength of from390 to 430 nm, and ultraviolet laser diodes or LEDs having a wavelengthof from 200 to 390 nm. Laser diodes are preferred violet or ultravioletlasers. The exposure dosage is preferably from 1 to 2000 μJ/cm² (0.001to 2 mJ/cm²), more preferably from 5 to 500 μJ/cm², and most preferablyfrom 20 to 200 μJ/cm², depending on the sensitivity of thephotosensitive layer. Violet laser with a wavelength of from 390 to 430nm is particularly useful among violet and ultraviolet lasers.

Laser imaging devices are currently widely available commercially. Anydevice can be used which provides imagewise laser exposure according todigital imaging information. Commonly used imaging devices includeflatbed imager, internal drum imager, and external drum imager, all ofwhich can be used for the imagewise laser exposure in this invention.

The on-press developable plate is usually exposed on an exposure device,and then mounted on press to develop with ink and/or fountain solutionand then print out regular printed sheets. However, the plate can alsobe exposed on a printing press (such as by mounting on the platecylinder or sliding through a flatbed imager mounted on the press), andthe exposed plate can be directly developed on press with ink and/orfountain solution and then print out regular printed sheets. The inkand/or fountain solution solubilized or dispersed photosensitive layerand/or overcoat can be mixed into the ink and/or the fountain solutionon the rollers, and/or can be transferred to the blanket and then thereceiving medium (such as paper). The fountain solution roller isengaged (to the plate cylinder as for conventional inking system or tothe ink roller as for integrated inking system) for preferably 0 to 100rotations, more preferably 1 to 50 rotations and most preferably 5 to 20rotations (of the plate cylinder), and the ink roller is then engaged tothe plate cylinder for preferably 0 to 100 rotations, more preferably 1to 50 rotations and most preferably 5 to 20 rotations before engagingthe plate cylinder and feeding the receiving medium (such as paper).Good quality prints should be obtained preferably under 40 initialimpressions, more preferably under 20 impressions, and most preferablyunder 5 impressions.

The ink and fountain solution may be applied at any combination orsequence, as needed for the plate; there is no particular limitation.For conventional wet press, usually fountain solution is applied (tocontact the plate) first, followed by contacting with ink roller;preferably, fountain solution is applied to the plate first to dampenwithout removing the photosensitive layer, followed by contacting withink to remove the non-hardened areas of the photosensitive layer. Forpress with integrated inking/dampening system, the ink and fountainsolution are emulsified by various press rollers before beingtransferred to the plate as emulsion of ink and fountain solution.

The plate may be rinsed or applied with an aqueous solution, includingwater and fountain solution, to remove the water soluble or dispersibleovercoat (for plate with an overcoat) and/or to dampen withoutdeveloping the plate, after imagewise exposure and before on-pressdevelopment with ink and/or fountain solution.

The ink used in this application can be any ink suitable forlithographic printing. Most commonly used lithographic inks include “oilbased ink” which crosslinks upon exposure to the oxygen in the air and“rubber based ink” which does not crosslink upon exposure to the air.Specialty inks include, for example, radiation-curable ink and thermallycurable ink. An ink is an oleophilic, liquid or viscous material whichgenerally comprises a pigment dispersed in a vehicle, such as vegetableoils, animal oils, mineral oils, and synthetic resins. Variousadditives, such as plasticizer, surfactant, drier, drying retarder,crosslinker, and solvent may he added to achieve certain desiredperformance. The compositions of typical lithographic inks are describedin “The Manual of Lithography” by Vicary, Charles Scribner's Sons, NewYork, and Chapter 8 of “The Radiation Curing: Science and Technology” byPappas, Plenum Press, New York, 1992.

The fountain solution used in this application can be any fountainsolution used in lithographic printing. Fountain solution is used in thewet lithographic printing press to dampen the hydrophilic areas(non-image areas), repelling ink (which is hydrophobic) from theseareas. Fountain solution contains mainly water, generally with additionof certain additives such as gum arabic and surfactant. Small amount ofalcohol such as isopropanol can also be added in the fountain solution.Water is the simplest type of fountain solution. Fountain solution isusually neutral to mildly acidic. However, for certain plates, mildlybasic fountain solution is used. The type of fountain solution useddepends on the type of the plate substrate as well as the plate. Variousfountain solution compositions are described in U.S. Pat. Nos. 4,030,417and 4,764,213.

Emulsion of ink and fountain solution is an emulsion formed from ink andfountain solution during wet lithographic printing process. Becausefountain solution (containing primarily water) and ink are not miscible,they do not form stable emulsion. However, emulsion of ink and fountainsolution can form during shearing, compressing, and decompressingactions by the rollers and cylinders, especially the ink rollers andplate cylinder, on a wet lithographic press. For wet press withintegrated inking system, ink and fountain solution are emulsified onthe ink rollers before transferred to the plate.

The plate of this invention is on-press developed with ink and/orfountain solution. Preferably, the plate is a wet plate which ison-press developed with ink and/or fountain solution, or a waterlessplate which is on-press developed with ink. More preferably, the plateis a wet plate which is on-press developed with ink and/or fountainsolution. Most preferably, the plate is a wet plate with oleophilicphotosensitive layer and hydrophilic substrate and is on-press developedwith ink and fountain solution.

This invention is further illustrated by the following examples of itspractice. Unless specified, all the values are by weight.

EXAMPLES 1-5

An electrochemically roughened, anodized, and polyvinylphosphonic acidtreated aluminum sheet was first coated with a 0.1% aqueous solution ofpolyvinyl alcohol (Celvol 540, from Celanese) with a #6 Meyer rod,followed by drying in an oven at 100° C. for 2 min. The polyvinylalcohol coated substrate was further coated with the photosensitivelayer formulation PS-1 with a #8 Meyer rod, followed by drying in anoven at 90° C. for 2 min.

PS-1 Weight Component ratios Neocryl B-728 (Polymer from Zeneca) 3.193Sartomer SR-399 (Acrylic monomer from Sartomer) 7.630 Pluronic L43(Nonionic surfactant from BASF) 0.6492,2-Bis(2-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole 1.4072-Mercaptobenzoxazole 0.839 4,4′-Bis(diethylamino)benzophenone 0.2812-Butanone 86.000

The photosensitive layer coated plate was further coated with awater-soluble overcoat OC-1 using a #6 Meyer rod, followed by drying inan oven at 100° C. for 2 min.

OC-1 Component Weight ratios Airvol 205 (polyvinyl alcohol from AirProducts) 0.40 Dioctyl sulfosuccinate sodium salt (surfactant) 0.02Water 99.58

The plate was exposed with a violet plate imager equipped with a 30 mwviolet laser diode emitting at about 405 nm (MAKO-4 from ECRM) for adosage of about 60 μJ/cm². The plate was imaged in a dim red light room,and was kept in a light tight box before and after imaging.

The laser exposed plate was cut into five pieces, and each piece waswrapped with a separate aluminum foil. Each piece of the plate wastested on press under a different Lighting condition. The first piecewas tested in the dark (with all lights turned off). The second piecewas tested under a 60-watt yellow light (yellow coated incandescentlight, from General Electric). The third piece was tested under a60-watt red light (red coated incandescent light, from GeneralElectric). The fourth piece was tested under a 20-watt white officefluorescent light (from General Electric). The fifth piece was testedunder a 100-watt regular incandescent light (for home use, from GeneralElectric). Each light was about 2 meters from the top of the press. Ittook about 5 minutes to mount each plate and start up the press.

Each of the exposed plate pieces was unwrapped and tested on a wetlithographic press (AB Dick 360) under the above described lightingcondition (including dark). The plate was directly mounted on the platecylinder of the press. After starting the press, the fountain roller wasengaged for 20 rotations, the ink roller (carrying emulsion of ink andfountain solution) was applied to the plate cylinder for 20 rotations,and the plate cylinder was then engaged with the blanket cylinder andprinted with paper. The printed sheets were evaluated for the on-pressdevelopability of the plates, with the results summarized in Table 1.

TABLE 1 Background at Inking in Background at 200 imaging Pressroomlighting 20 impressions impressions areas In the dark (no light) CleanClean Good Yellow light Clean Clean Good Red light Clean Clean GoodWhite fluorescent light Inked Heavy toning Good Regular incandescentlight Inked Heavy toning Good

EXAMPLES 6-10

An electrochemically roughened, anodized, and silicate treated aluminumsheet was coated with thermosensitive layer formulation PS-2 using a #8Meyer rod, followed by drying in an oven at 90° C. for 2 min.

PS-2 Component Weight ratios Neocryl B-728 (Polymer from Zeneca) 2.73Sartomer SR-399 (Acrylic monomer from Sartomer) 6.52 Pluronic L43(Nonionic surfactant from BASF) 0.562,4-Bis(trichloromethyl)-6-[(4-ethoxyethylenoxy)-phen- 1.001-yl]-s-triazine ADS-830AT (Infrared absorbing cyanine dye from 0.10American Dye Source) Acetone 90.0

The thermosensitive layer coated plate was further coated with awater-soluble overcoat OC-2 using a #6 Meyer rod, followed by drying inan oven at 100° C. for 2 min.

OC-2 Component Weight ratios Airvol 205 (Polyvinyl alcohol from AirProducts) 5.00 Zonyl FSO (Perfluorinated surfactant from DuPont) 0.02Water 95.00

The plate was exposed with an infrared laser plate imager equipped withlaser diodes emitting at about 830 nm (Trendsetter from Creo) at adosage of 150 mJ/cm². The plate was imaged in a dim red light room, andwas kept in a light tight box before and after imaging.

The laser exposed plate was cut into five pieces, and kept in alight-tight box for all the time except for the specific exposure asindicated. The first piece was kept in the dark (in a box) all the timeafter exposure. The second piece was exposed to a 60-watt yellow light(yellow coated incandescent light, from General Electric) at a distanceof 2 meters for 60 minutes. The third piece was exposed to a 60-watt redlight (red coated incandescent light, from General Electric) at adistance of 2 meters for 60 minutes. The fourth piece was exposed to a40-watt white office fluorescent light (from General Electric) at adistance of 2 meters for 60 minutes. The fifth piece was exposed to a100-watt regular incandescent light (for home use, from GeneralElectric) at a distance of 2 meters for 60 minutes.

The exposed plate pieces as treated above were tested on a wetlithographic press (AB Dick 360) under a dim red light. The plate wasdirectly mounted on the plate cylinder of the press. After starting thepress, the fountain roller was engaged for 20 rotations, the ink roller(carrying emulsion of ink and fountain solution) was applied to theplate cylinder for 20 rotations, and the plate cylinder was then engagedwith the blanket cylinder and printed with paper. The printed sheetswere evaluated for the on-press developability of the plates, with theresults summarized in Table 2.

TABLE 2 Background Inking in Room light exposure before Background at at200 imaging mounting on press 20 impressions impressions areas In thedark (no exposure) Clean Clean Good Yellow light for 60 minutes CleanClean Good Red light for 60 minutes Clean Clean Good White officefluorescent light Inked Heavy Good for 60 mintues toning Regularincandescent light Inked Heavy Good for 60 minutes toning

1. A method of lithographically printing images on a receiving medium,comprising in order: (a) providing a lithographic printing platecomprising (i) a substrate, and (ii) a photosensitive layer soluble ordispersible in ink and/or fountain solution and capable of hardeningupon exposure to a laser having a wavelength selected from 200 to 1200nm; wherein said photosensitive layer exhibits an affinity or aversionsubstantially opposite to the affinity or aversion of said substrate toat least one of ink and fountain solution; (b) imagewise exposing saidplate with said laser to cause hardening of the photosensitive layer inthe exposed areas; (c) developing said exposed plate with ink and/orfountain solution on a lithographic press to remove the non-hardenedareas of said photosensitive layer; and (d) lithographically printingimages from said plate to the receiving medium; (e) wherein at least 90%by time of said on-press development (step c) is performed with theplate under a yellow-red light or in substantial darkness; and at least90% by time of said lithographic printing (step d) is performed with theplate under white light.
 2. The method of claim 1 wherein at least 90%by time of said step (b) is performed with the plate under a yellow-redlight or in substantial darkness.
 3. The method of claim 1 whereinsubstantially the entire step (c) is performed with the plate under ayellow-red light, and substantially the entire step (d) is performedwith the plate under white light.
 4. The method of claim 1 whereinsubstantially the entire steps (b) and (c) are performed with the plateunder a yellow-red light, and substantially the entire step (d) isperformed with the plate under white light.
 5. The method of claim 1wherein at least 90% by time of said step (c) is performed with theplate under a yellow-red light.
 6. The method of claim 1 wherein saidsteps (c) and (d) are performed in a pressroom having a yellow-red lightsource and a white light source, the yellow-red light source is on andthe white light source is off during at least 90% by time of said step(c), and the white light source is on during at least 90% by time ofsaid step (d).
 7. The method of claim 1 wherein said steps (c) and (d)are performed in a pressroom having a yellow-red light source and awhite light source, the yellow-red light source is turned on and thewhite light source is turned off at or before the start of said step(c), and the white light source is turned on around the end of said step(c).
 8. The method of claim 1 wherein said plate is imagewise exposedwith said laser on said press which is shielded with covers to block offsubstantially all of the room light from reaching the plate mounted onsaid press for at least 90% by time of said steps (b) and (c), and saidcovers are opened during at least 90% by time of said step (d).
 9. Themethod of claim 1 wherein said photosensitive layer comprises a freeradical polymerizable monomer, a free radical initiator, and asensitizing dye.
 10. The method of claim 1 wherein said photosensitivelayer is oleophilic and said substrate is hydrophilic.
 11. The method ofclaim 1 wherein said plate further comprises a water soluble ordispersible overcoat.
 12. The method of claim 1 wherein said laser is aviolet or ultraviolet laser having a wavelength selected from 200 to 430nm.
 13. The method of claim 1 wherein said laser is an infrared laserhaving a wavelength selected from 750 to 1200 nm.
 14. A method oflithographically printing images on a receiving medium, comprising inorder: (a) providing a lithographic printing plate comprising (i) asubstrate, and (ii) a photosensitive layer soluble or dispersible in inkand/or fountain solution and capable of hardening upon exposure to alaser having a wavelength selected from 200 to 1200 nm; wherein saidphotosensitive layer exhibits an affinity or aversion substantiallyopposite to the affinity or aversion of said substrate to at least oneof ink and fountain solution; (b) imagewise exposing the plate with saidlaser to cause hardening of the photosensitive layer in the exposedareas; (c) developing said exposed plate with ink and/or fountainsolution on a lithographic press to remove the non-hardened areas of thephotosensitive layer; and (d) lithographically printing images from saidplate to the receiving medium; (e) wherein said steps (c) and (d) areperformed in a pressroom having a yellow-red light source and a whitelight source; the yellow-red light source is on and the white lightsource is off during at least 90% by time of said step (c), and thewhite light source is on during at least 90% by time of said step (d).15. The method of claim 14 wherein the yellow-red light source is on andthe white light source is off during substantially the entire step (c),and the white light source is on during substantially the entire step(d).
 16. The method of claim 14 wherein said step (b) is performed witha laser exposure device in said pressroom, said yellow-red light sourceis on and said white light source is off during substantially the entiresteps (b) and (c), and said white light source is on duringsubstantially the entire step (d).
 17. The method of claim 14 whereinthe room light sources are controlled, at least manually and/orelectronically, with at least one controlling center which is capable ofswitching (i) the yellow-red light source on and the white light sourceoff, (ii) the white light source on and the yellow-red light source off,or (iii) both the yellow-red light source and the white light sourceoff.
 18. The method of claim 14 wherein the yellow-red light source isturned on and the white light source is turned off at or before thestart of step (b), and the white light source is turned on around theend of step (c).
 19. The method of claim 14 wherein the plate isimagewise exposed with said laser off press on an exposure device insaid pressroom; and the light sources are controlled at least from (i)the exposure device which is capable of automatically turning off thewhite light source, if it is on, and turning on the yellow-red lightsource, if it is off, after setting up and until at least completing alaser exposure job; and (ii) the press which is capable of automaticallyturning on the white light source after starting the press for 1 to 600rotations of the plate cylinder or for 1 to 600 seconds; wherein if theexposure device has a job in the queue, is exposing a plate, or has anexposed plate on it waiting to be removed, the light switching functionof the press will postpone until the exposure device finishes the joband the exposed plate on the exposure device has been removed for 0 to600 seconds.
 20. The method of claim 14 wherein the plate is imagewiseexposed with said laser off press on an exposure device which has coversto block off substantially all of the room light from reaching the plateloaded on said exposure device; the yellow-red light is turned on, if itis off, and the white light is turned off, if it is on, before or whenpicking up an exposed plate from the exposure device; and the whitelight source is then turned on after loading said exposed plate on saidpress and starting said press for 1 to 600 rotations of the platecylinder or for 1 to 600 seconds.
 21. The method of claim 14 wherein theplate is imagewise exposed with said laser on said press; and the lightsources are controlled at least from said press which (i) is capable ofautomatically turning off the white light source, if it is on, andturning on the yellow-red light source, if it is off, after setting up alaser exposure job and until completing the laser exposure and thenengaging the fountain roller and/or the ink roller to the plate cylinderfor 1 to 600 rotations of the plate cylinder or for 1 to 600 seconds,and (ii) is capable of automatically turning on the white light afterstarting the press for 1 to 600 rotations of the plate cylinder or for 1to 600 seconds.
 22. The method of claim 14 wherein the plate isimagewise exposed with said laser on said press; and the light sourcesare controlled at least from an electronic switch or computer program onthe press which (i) automatically turns on the yellow-red light source,if it is off, and turns off the white light source, if it is on, aftersetting up the laser exposure job; and (ii) automatically turns on thewhite light source after starting the press for 1 to 600 rotations ofthe plate cylinder or for 1 to 600 seconds.
 23. The method of claim 14wherein said pressroom is substantially dark if both the yellow-redlight source and the white light source are off.
 24. The method of claim14 wherein there are one or more presses and one or more exposuredevices in said pressroom; and the light sources are controlled at leastfrom (i) the exposure devices which are capable of automatically turningoff the white light source, if it is on, and turning on the yellow-redlight source, if it is off, after setting up and until at leastcompleting a laser exposure job; and (ii) the presses which are capableof automatically turning on the white light source after starting thepress for 1 to 600 rotations of the plate cylinder or for 1 to 600seconds; wherein if any of the exposure devices has a job in the queue,is exposing a plate, or has an exposed plate on it waiting to beremoved, the light switching function of the presses will postpone untilthe exposure device finishes the job and the exposed plate on theexposure device has been removed for 0 to 600 seconds.
 25. A method oflithographically printing images on a receiving medium, comprising inorder: (a) mounting onto the plate cylinder of a lithographic press alithographic printing plate comprising (i) a substrate, and (ii) aphotosensitive layer soluble or dispersible in ink and/or fountainsolution and capable of hardening upon exposure to a laser having awavelength selected from 200 to 1200 nm; wherein said photosensitivelayer exhibits an affinity or aversion substantially opposite to theaffinity or aversion of said substrate to at least one of ink andfountain solution; (b) imagewise exposing the plate with said laser tocause hardening of the photosensitive layer in the exposed areas; (c)developing said exposed plate with ink and/or fountain solution on saidpress to remove the non-hardened areas of the photosensitive layer; and(d) lithographically printing images from said plate to the receivingmedium; (e) wherein said press is in a pressroom having a yellow-redlight source and a white light source; the yellow-red light source is onand the white light source is off during at least 90% by time of saidsteps (a) to (c), and the white light source is on during at least 90%by time of said step (d).
 26. The method of claim 25 wherein theyellow-red light source is on and the white light source is off duringsubstantially the entire steps (a) to (c), and the white light source ison during substantially the entire step (d).